Food Intolerance

A food intolerance is a reaction to certain ingredients (such as gluten or sugar) found in foods. Food intolerances are not food allergies. Food allergies result when a food component (usually a protein) causes the immune system to react, leading to symptoms such as hives, wheezing, diarrhea, or shortness of breath. While food intolerances can cause abdominal pain or diarrhea, they are not caused by the immune system reacting to a food. 

Food intolerance can be categorized into three types: enzyme deficiencies, pharmacological effects, and unknown. 

• Enzyme deficiencies may result in an inability to break down a food ingredient. An example is lactose intolerance, where the body is missing the enzyme that digests lactose (milk sugar). In people with lactose intolerance (see GIKids handout), the inability to break down milk sugar results in diarrhea, pain, and gas. 
• Pharmacologic intolerance is due to the presence of certain chemicals in foods that can cause gastrointestinal symptoms. For example, a person who drinks too much caffeine may have symptoms of heartburn or diarrhea. 
• Unknown, also called idiopathic, reactions indicate that the way a food item causes symptoms is unknown. 

In contrast to food allergies, food intolerances are not life-threatening. Most individuals with food intolerances can tolerate small amounts of the trigger food in their diet without symptoms, but some individuals are very sensitive and must eliminate that food from the diet completely.

identifying as having reactions to a food. However, the true prevalence of food intolerances is likely closer to 2%–4%. For comparison, the rate of food allergies is 4%–7% in children.

Individuals with irritable bowel syndrome (IBS), a condition common in teenagers and young adults, have symptoms of abdominal pain, bloating, and diarrhea. Patients with IBS commonly report food intolerances, particularly to certain sugars called FODMAPs. FODMAPs is an acronym for fermentable oligo-, di-, monosaccharides, and polyols. They occur naturally in plant-based foods, dairy-based foods, and sweeteners. FODMAP sugars include lactose, fructose, fructans (found in many vegetables, wheat, barley, rye), galactans (found in beans and pulses), polyols (found in many fruits), and artificial sweeteners. Thus, a low-FODMAP diet excludes certain foods, including many fruits (such as apples and cherries), beans, dairy, onions, and garlic.

Symptoms of a food intolerance include diarrhea, bloating, abdominal discomfort, and increased gas production that may occur within hours of eating an offending food item. The symptoms are usually short-term, lasting minutes to hours after eating the food.

Keeping a detailed dietary and symptom history is a useful first step to identify potential food triggers. Limited testing is available to diagnose food intolerances. Breath testing may be used to diagnose difficulties digesting lactose (milk sugar) and fructose (fruit sugar) malabsorption (see GIKids handout on lactose breath testing). 

In some patients with gastrointestinal symptoms, an endoscopy may help diagnose carbohydrate malabsorption and also exclude other causes of symptoms. During an endoscopy, the doctor may take a small biopsy to measure enzymes that break down milk and fruit sugars. 

The best way to diagnose a food intolerance is to eliminate the suspected food and see if the symptoms completely resolve. Once the symptoms resolve, reintroduce that suspected food to see if symptoms recur. 

There are several commercially available tests that claim to diagnose food intolerances. Use of these tests is discouraged, because there is no medical evidence that says these tests can accurately identify food intolerances.

Long-term management of food intolerances involves avoiding the foods suspected to cause adverse reactions. Complete symptom resolution occurs when these food items are avoided.

There is complete resolution of symptoms with dietary elimination of suspected foods. While food intolerances can cause discomfort and affect quality of life, they do not result in gastrointestinal damage. Patients with clear food intolerances often have a good quality of life if they restrict the foods that cause symptoms.

Author: Anil Kesavan, MD
Editor: Athos Bousvaros, MD
March 2021